DESCRIPTION The Postfix mail system uses optional lookup
tables. These tables are usually in dbm or db format.
Alternatively, lookup tables can be spec- ified in CIDR
(Classless Inter-Domain Routing) form. In this case, each
input is compared against a list of patterns. When a match
is found, the corresponding result is returned and the
search is terminated.

To find out what types of lookup tables your Postfix
system supports use the "postconf -m" command.

To test lookup tables, use the "postmap -q"
command as described in the SYNOPSIS above.

TABLE FORMAT The general form of a Postfix CIDR table
is:

network_address/network_mask result When a search string
matches the specified network block, use the corresponding
result value. Specify 0.0.0.0/0 to match every IPv4 address,
and ::/0 to match every IPv6 address.

An IPv4 network address is a sequence of four decimal
octets separated by ".", and an IPv6 network
address is a sequence of three to eight hexadecimal octet
pairs separated by ":".

Before comparisons are made, lookup keys and table
entries are converted from string to binary. Therefore table
entries will be matched regardless of redundant zero
characters.

Note: address information may be enclosed inside
"[]" but this form is not required.

IPv6 support is available in Postfix 2.2 and later.

network_address result When a search string matches the
specified network address, use the corresponding result
value.

blank lines and comments Empty lines and whitespace-only
lines are ignored, as are lines whose first non-whitespace
character is a #.

multi-line text A logical line starts with
non-whitespace text. A line that starts with whitespace
continues a logical line.

TABLE SEARCH ORDER Patterns are applied in the order as
specified in the table, until a pattern is found that
matches the search string.